Too many to mention...
For Frederick the Great's army in the Seven Years War, Christopher Duffy's "The Army of Frederick the Great" is an excellent book to have, both on its own, if it's the only such book you might read; but also as a starting point. You can following his bibliography for the original sources he used. Many of his sources were memoirs, diaries, letters, and Frederick's own writings.
Duffy's book on the Austrian army of the time is also an excellent book. "Instrument of War: the Army of Maria Theresa" is similar to the book on Frederick's army, except bigger. Duffy reworked the book into a 2-volume addition, as more information became available in the 90s after the dissolution of the Soviet bloc.
Hans Bleckwenn's cassette on the Prussian army's uniforms is also an excellent resource, not only for the illustrations, but for the content, details about each unit detailed.
And more recently, Daniel Hohrath's "Frederick the Great: Uniforms of the Prussian Army, 1740-1786" is outstanding, with its extensive research, and photographs of existing pieces, and recovered photos of items that were destroyed in WWII. These are excellent references for painters.
I have the KLIO's book, "The Armies of the Warring States, 1756-1763", which was long on my search list, and represents a huge effort on the part of the editors. But I found in the meantime that some of the content is outdated, based on other sources I've found.
Ortmann's book on the Brunswick army is an excellent reference on that subject, because he had access to local sources. The Brunswick army in the Seven Years War is one of my specific subjects of interest, so it was a real prize for me when I found a copy.
And I have a biography of Frederick William I, whose author and title escape me. But it's a good book that gets past the caricature that most people have in their minds of the Soldier King. Not quite the brutal buffoon many picture.
For World War II, I have a lot of books I can recommend...
James Hornfischer's "Neptune Rising", "The Last Stand of the Tin Can Sailors", and "The Fleet at Flood Tide: America at Flood Tide 1944-1945" are excellent books to read. (I only learned a week ago that Hornfischer passed away in 2021, a sad loss!)
On Midway, "Shattered Sword" is an excellent book, replacing Prange's "Miracle at Midway" because of Fuchida's distortions; Lord's "Incredible Victory" is still a good book to read, for the stories of the participants. He's not as tainted by the "fateful five minutes" fable as Prange, either. Craig Symonds' more recent "The Battle of Midway" focuses on the intelligence coup the US Navy scored and is also an excellent book to read to round out an understand of the battle.
John Lindstrom's "First Team" series is also an excellent series of books to read about the US Navy in the first year of the Pacific War. His research provided new insights, or perhaps deeper insights, to the common knowledge in our history writing up to the 90s.
I enjoy Cornelius Ryan's three books, "The Longest Day", "A Bridge Too Far", and "The Last Battle". As with Lord's books, I enjoy the participants' stories and perspectives on the broader battle.
I enjoy Stephen Ambrose's books, too, though I haven't read everything in his pretty extensive catalog. "Band of Brothers" (naturally), "Citzen Soldiers", "The Victors" are in my library and I re-read them from time to time.
"Doomed at the Start" on the USAAF in the Philippines during the Japanese invasion is another one I can recommend, on a subject that isn't often covered.
I'll have to catalog the rest of the ones I have.
I'll add Victor Davis Hanson's books, too, from "The Second World Wars" to "A War Like No Other", on the Peloponnesian War; "The Soul of Battle" which looks at the qualities of mavericks from Epaminondas to Sherman to Patton; "The Savior Generals", which follows the themes in "Soul of Battle" to an expanded list of examples. "The Dying Citizen" is also an excellent look at the concept of citizenship from its origins in Ancient Greece down to the present. Some day, I'll get through his entire catalog. I enjoy his approach as a classicist who notes the parallels between classical society and today. As some say, history might not repeat itself, but it does rhyme.
Off the top of my head, I can't think of too many more. Some older books like Martin Caidin's "Ragged Rugged Warriors" (thanks to Scott Hershbell, oldtrousers, for that copy) and "Flying Fortresses", Robert L Scott's "God is My Co-Pilot", books I read as a kid as my interest in World War II sprouted and blossomed.
And as far as references go, a lot of Squadrons and Ospreys, which some might not count. But I'll pull one of those out just to read.
I probably should catalog my library...
Prost!
Brad